Separation of acetylene from gaseous mixtures by glycolonitrile



s. P. ROBINSON 2,659,453 SEPARATION OF ACETYLENE FROM GASEOUS MIXTURES BY GLYCOLONITRILE Filed Dec. 20, 1948 Nov. 17, 1953 HEATER COOLER mmmmOwm INVENTOR. s. Pv ROBINSON BY X ATTOR/VE 5 48 COOLER F/G. Z.

3 4 il mwmmowm Patented Nov. 17, 1953 NEED STATE AEENT OFFICE sam r. Robinson,

Bartlesville, Okla, assignor to Phillips Petroleum Company, a corporation of Delaware Application December 20, 1948, Serial N 0. 66,403 '13 Claims. (01. 183-115) This invention relates to the separation of acetylenefrom gaseous mixtures containing this compound. In one of its more specific aspects, it relates to a process for the separation and recovery of acetylene from acetylene-containing gases wherein an aqueous solution of glycolonitrile (HOCHzCN) is used as the selective solvent.

The process of this invention comprises contacting a gaseous mixture containing acetylene with glycolonitrile and subsequently separating the absorbed hydrocarbon from the absorption liquid. The contacting operation may be conducted under substantially atmospheric conditions of pressure and temperature, but preferably should be conducted under pressures greater than atmospheric pressure. The absorbed hydrocarbons may be separated from thesolvent by stripping at lower pressures and/or higher temperatures than those employed in the contacting step, or by other known means such as contact ing the rich glycolonitrile solution with a second solvent which is selective for either the hydrocarbon or the glycolonitrile.

An object of this invention is to provide a process for the separation and. recovery of acetylene from gaseous mixtures containing this compound.

Another object of my invention is to provide a process for the extraction and recovery of acetylene from gaseous mixtures containing acetylene wherein a relatively small volume of absorbent is required. 7

Still other objects and advantages of my invention will be obvious to those skilled in the art u'p'on reading the following specification,

In the drawing, Figure l is a diagrammatic representation of one form of apparatus in which one embodiment of my invention may be practiced. Figure 2 is a diagrammatic representa- "on of another form of apparatus in which a second embodiment of my invention may be practiced.

My invention comprises intimately contacting an acetylene-containing gas with a water solution of glycolonitrile under absorption conditions, then exposing the enriched absorbent to conditions under which the absorbed hydrocarbon is liberated or otherwise separated from the solvent. Such gases as refinery cracked gases, residue gases from various processes, or gases resulting from partial combustion of hydrocarbons and which contain acetlyene are adaptable for treatment in my process with my novel absorbent. The aforementioned refinery cracked gases may result from cracking operations in tages or m process which the normal gaseous compounds are not inchided in final gasoline boiling range products. Gases resulting from partial combustion of hydrocarbons may be such gases as are normally disposed of to the atmosphere, as, for example, in process for the production of carbon black by furnace methods. In such latter process, hydi'oca'rbon charge stocks are ordinarily partially burned to supply sufiicient heat for the conversion of the remainder of the hydrocarbons to earbon black, and under such partial combustion conditions appreciable quantities of acetylene and ethylene, along with gases normally produced by combustion, are formed. One of the main advanis that such gases as these may be treated for recovery of valuable acetylene;

the operation of iny process, such an unsaturated hydrocarbon-containing gas is contacted with an aqueous solution of glycolonitrile. This process may preferably be operated continuously and in such an operation the absorbent is introduced into a vertically disposed absorption tower at a point near its top, while the gas to be treated is introduced into the tower at a point near its bottom. Such gas-liquid contactmg apparatus as b afiles, slats or bubble trays and caps may be used for efficient contacting between the absorbent and the gas. Residue gas substantially free of acetylene is removed from the top of this absorption vessel and may be passed to such disposal as desired. In case the gas contains saturated hydrocarbons, such as methane or ethane, or other hydrocarbons, or even car-'- bon monoxide and hydrogen, it still may be valuable as a source of fuel. The nitrile solution reaching the bottom of the contacting vessel is removed therefrom with its charge of dissolved gas and it is preferably passed into a heat exchanger or other heater for raising its temperature prior to introduction into a stripping vessel. Thisvessel is preferably maintained at a pres= s'ure below that of the contacting apparatus. For the stripping operation, the heated enriched nitrile is introduced into the top of the still or stripper vessel. The interior of this vessel may contain gas-liquid contacting equipment similar to that normally used in absorption vessels. When the nitrile solution reaches the bottom of this stripper vessel it is free or substantially free of absorbed hydrocarbon and the lean absorbent then may be cooled in a cooler or be passed in heat exchange relation with the rich absorbent. The cooled lean absorbent may preferably be funther cooled to atmospheric or below atmospheric temperature, or to any desired temperature and then passed into the top of the absorption vessel to complete its cycle.

In the stripping operation, it is preferable to use a low boiling, normally liquid hydrocarbon as the stripping agent since the absorbed hydrocarbon is readily separated therefrom by a simple fractionation step. Steam may also be used as a stripping agent, preferably at subatmospheric pressure so as to minimize hydrolysis or decomposition of the glycolonitrile. It is preferable to operate the absorption step at a pressure greater than atmospheric pressure since at higher pressures less absorption liquid is required. If a high pressure is used in the aborption step the stripping operation may, if desired, consist merely of reducing the pressure on the rich absorbent under which condition absorbed gases are evolved from the solution. However, usually by mere reduction of pressure not all of the absorbed gases are removed and it is usually preferable to employ a stripping medium or to use other means of separation. In case the rich absorption liquid is heated for stripping of the absorbed hydrocarbon, and further, especially if open steam is used in the stripping step, water may be removed from or added to the nitrile solution. Hence, the concentration of nitrile in the absorption solution should be controlled by the operator.

Referring to the drawing, Figure 1 illustrates apparatus in which the above-described absorption-stripping operation using the solvent of my invention may be carried out. Absorber H is a conventional absorber into which is passed the acetylene containing feed stock through line l2. Residue gas leaves the absorber through an overhead line 53. Lean absorbent is introduced into the absorber through line |4 near the top of the vessel. Rich absorbent, aqueous glycolonitrile containing acetylene in solution, leaves the absorber through line 15, is heated in heater l7 and passes on through line 2|) containing valve 3| into a still 2|. Still 2| is a still of conventional design containing a reflux coil 29, a stripping gas inlet line 23, a bottoms outlet line l8 and an overhead line 22. Acetylene separated in this still from the absorbent passes through the overhead line 22 through a condenser 24 into an accumulator 25. Gaseous acetylene is passed from this accumulator through line 26 to any disposal desired. Water or aqueous nitrile solution in the recovered acetylene is condensed in condenser 24. Condensate is recycled from the accumulator through line 21 containing valve 33, through a cooler 28 and line l4 into the absorber Makeup water, glycolonitrile, or both these materials, may be added through line 30 as required. When steam is used as the stripping agent in still 2|, as disclosed hereinabove, an excess of water may accumulate in accumulator 25 so that water may need to be withdrawn from the system through line 21, valve 33 and line 30. In case a low boiling normally liquid hydrocarbon is used as a stripping agent, as disclosed hereinabove, it is introduced into the still 2| through line 23. This hydrocarbon is condensed in condenser 24 and condensate accumulates in accumulator 25. This liquid hydrocarbon will then float as a separate layer upon the surface of any water in accumulator 25 and this normally liquid hydrocarbon is removed from the accumulator through line 34 and it is vaporized in a heater, not shown, and the vapor recycled into the still 2| through line 23 as mentioned. When the separation operation in the vessel 2| is carried out merely by reducing pressure on the rich absorbent, as mentioned, the

rich absorbent is passed through line I5 from the absorber, through line 20 and the pressure re ducing valve 3| into the vessel 2|. In this case the heater i1 is omitted when the acetylene is removed from the absorbent in vessel 2| by pressure reduction alone. The operation is substantially one of flashing, and this type of operation for acetylene recovery is not preferred since, as mentioned above, the acetylene is not completely removed from the absorbent.

Other methods which may be used for separating and recovering the acetylene from the glycolonitrile solution include the use of secondary solvents for either the hydrocarbon or the nitrile. Thus the rich absorbent may be contacted with benzene in a second contacting zone, followed by separation into two liquid phases. The lower, aqueous phase contains the denuded glycoloni-- trile and may be recycled to the first contacting vessel for reuse in the process, while the upper, benzene-rich phase contains the unsaturated hydrocarbon which may then be recovered easily by fractional distillation. Alternatively, the rich absorbent may be treated with additional water, preferably at or near atmospheric pressure, to aid in releasing the absorbed hydrocarbons. The dilute glycolonitrile solution may then be reconcentrated to the desired concentration by distillatic-n, and reused in the process. Obviously, other materials in which hydrocarbons are soluble and which are substantially immiscible with aqueous glycolonitrile may be substituted for benzene.

Figure 2 of the drawing represents the embodiment of my invention in which a secondary solvent, such as benzene, is used to separate the acetylene from the rich absorbent. According to this embodiment, the absorber 4| with its feed gas inlet line 42, overhead gas outlet line 43, lean absorbent inlet line 44 and rich absorbent outlet line 45 are exactly like the corresponding absorber apparatus parts in Figure l. The aqueous glycolonitrile is introduced into the absorber 4% through line 44 and the rich absorbent is passed through line 45 into an extractor vessel 46. In this vessel, a secondary solvent, such as the hereinbefore mentioned benzene, is introduced through line 48. In this vessel the benzene extracts the acetylene from the aqueous glycolonitrile and the rich benzene is passed through line 41, heater 52, and line 53 into a still 54-. This still may be operated in a conventional manner involving the use of stripping steam from pipe '63 and an overhead cooling coil 55. The separated acetylene is passed through line 55, cooler or condenser 5! and line 6| into an accumulator 58. Any water accumulating in this vessel may be withdrawn through line 59. Any benzene accumulatingin vessel 58 is passed through line 5i! containing valve 64, through cooler 49 and line 48 into the extractor vessel 46. Still bottoms consisting of secondary solvent is passed through line 5|, cooler 49 and line 48 into the extractor. Makeup secondary solvent as required is added through line 63. The acetylene recovered from the secondary solvent accumulates as a gas in the accumulator 58 and is withdrawn therefrom through line 60 and is passed to such disposal as desired. Makeup aqueous glycolonitrile is added to the lean absorbent inlet line 44 through line 62 as required.

Glycolonitrile is useful in my process as an aqueous solution containing from about 30 to about per cent, preferably about 50 per cent,

water by weight. This nitrile solution is rendered stable by addition of suflicient non-volatile mineral acid to give the aqueous solution a .pH of about '2 /2 to '3. Glyc'olc'niti'ile bolls "at about 183 0. (759 mm.) with slight decomposition, but in an aqueous solution in the presence of acid it is relatively stable and is accordingly suitable for commercial operation. Thus glycolonitrile in the presence of acid may be used in the still at it's boiling point. v

'I am aware of U. '5. 1,882,978, issued October 18, 1932, to Otto Schmidt and Otto 'Grcsskinsky, in which the compound lactonitrile (lactic acid nitrile, CHsCHO-HCN) is mentioned, along with numerous other organic compounds of various types, as a possible selective solvent for unsaturated hydrocarbons, particularly gaseous diol'efins such as butadiene. The compound lactonitrile, however, is not well suited 'to the separation of acetylene from gaseous mixtures because of its relatively low capacity for acetylene per unit of weight of the nitrile, and lactonitrile has never achieved success commercially as a selective solvent for acetylene.

I have found, however, that aqueous glycolonitrile has a significantly higher capacity for acetylene than does lactonitrile and is eminently suited to the process of this invention by reason of its high selectivity for acetylene as compared with ethane, ethylene and other gases with which acetylene is usually found in admixture.

Furthermore, glycolonitrile or its aqueous solutions may be used to advantage for the recovery of acetylene from gas streams in which the acetylene is present in very low concentrations. The recovery of acetylene from such streams by means of the more volatile conventional solvents (such as acetone) results in prohibitive losses of solvent in the overhead gases. This is not the case with either glycolonitrile or its aqueou solutions. Also, the concentrated aqueous solutions of glycolonitrile, or the anhydrous material, may be used to advantage at low temperatures because of their low freezing points.

The following tabulation gives some properties of glycolonitrile:

Density 1.104 at 19 C. Melting point Below 72 C. Boiling point 183 C. (slight decomposition) Solubility in water Very soluble. Solubility in alcohol Very soluble. Solubility in ether Very soluble. Solubility in benzene Insoluble.

The example given below shows the relative capacities, for acetylene, of aqueou solutions of glycolonitrile and lactonitrile. It also shows the high selectivity of glycolonitrile for acetylene as compared with ethane. The concentrations of the aqueous nitrile solutions are in per cent by weight in each case.

Lactonitrile Acetylene:

Volume of Liquid Sample, cc.. 8. 5 8.0 Volume Gas Dissolved at C.

747 mm., cc (c0. Gas/cc. liquid, gas at NTP).

Ethane:

Volume of Liquid Sample, cc ol. Gas dissolved at 25 0. 747

c1111., cc (cc. Gas/cc. llquid, gas at NTP).

sufficient phosphoric acid to give the solution a pH of "2.8. From the data of "these tests, it is seen that the glycolonitrile dissolved 1.93 cc. or a'ce'tyiene per cc. of absorbent liquid contrast to only more. of acetylene per cc. of the lactonitrile solution. rou hly speaking, about one-fourth less glycolonitrile solution by volume or by weight is required "for absorbing a given amount of acetylene than when usin the lactonitrile solution. This greater absorption of acetylene in the absorbent solution has many commercial advantages as, for exam le, les absorpti'on solution is required for a given acetylene production, the equipment is smaller, hence its cost in regard to purchase or constructionls less, and further, operation costs are smaller since smaller volumes of absorption liquid' need be um ed from the absorption vessel to the stri ping vessel and from the stri ping vessel back to the absorption vessel.

From the -solil'loility data of ethane in the glycolonitrile solution, it is seen that a substantially ethane-tree acetylene product may be produced in a i'n'ulti-stage separation system using my aqueous glycolonitrile solution. Ethylene, while more soluble in my solvent than is ethane, may also be substantially completely removed from acetylene by m process since it is much less soluble than acetylene.

It will be obvious to those skilled in the art that many variations and alterations in my process may be made and yet remain within the intended scope of my invention.

Having disclosed my invention, I claim:

1. A method for separating acetylene from admixture with gases withwhich acetylene is normally produced comprising contacting said admixture of gases with a reagent comprising an aqueous solution of glycolonitrile acidified with a nonvolatile mineral acid to a pH of 2 to 3, separating the resulting solution from the gases and recovering acetylene from said resulting solution.

A method for separating acetylene from adixture with gases with which acetylene normally occurs comprising contacting said admixture of gases with an aqueous solution of glycolonitrile acidified with a nonvolatile mineral acid to a pH of 2 /2 to 3, separating the resulting solution from the remaining gases and recovering the acetylene from said resulting solution.

3. A method for separating acetylene from admixture with gaseous hydrocarbons and recovering the acetylene in concentrated form which comprises intimately contacting the hydrocarbon mixture with a reagent comprising an aqueous solution of glycolonitrile acidified with a nonvolatile mineral acid to a pH of 2% to 3 at atmospheric temperature and under a superatmospheric pressure, separating the resulting acetylene-containing solution from undissolved gaseous hydrocarbons, exposing said separated solution to conditions of heat and reduced pressure and recovering the acetylene.

4. A method for separating acetylene from partial combustion products comprising acetylene, nitrogen, carbon monoxide, carbon dioxide, methane, ethylene and ethane, comprising contacting said partial combustion products continuously and in countercurrent relation to a stream of an aqueous solution of glycolonitrile having a pH in the range of 2 to 3 under superatmospheric pressure, exposing said contacted stream of aqueous glycolonitrile continuously to stripping conditions of pressure lower temperature of the boiling point of said aqueous glycolonitrile solution, separating acetylene containing moisture from said stripping operation and recovering the actylene as the product of the process.

5. The method of claim 4 wherein the actylene is dried of its moisture content and dry acetylene is recovered as the product of the process.

6. The method of claim 4 wherein the aqueous solution of glycolonitrile has a water content be tween the limits of and 80% by weight.

7. The method or" claim 4 wherein the aqueous solution of glycolonitrile has a water content of'50% by Weight.

8. A method for separating acetylene from admixture with other gases comprising intimately ous solution of glycolonitrile aci-difi d with a nonvolatile mineral acid to a pH of 2 to 3, separating the contacted gaseous mixture from said aqueous solution, contacting the separated aqueous solution with benezene and recovering the acetylene from the benzen 12. A method for separating acetylene from admixture with other gases'comprising intimately contacting the gaseous mixture with an aqueous I solution of glycolonitrile acidified with a nonvolatile mineral acid to a pH of 2%; to 3, separating the contacted gaseous mixture from the aqueous solution, contacting the separated aqueous contacting the gaseous mixture with an aqueous 7 solution of glycolonitrile,separating the contacted gaseous mixture from said aqueous solution, contacting the separated aqueous solution with benzene and recovering the actylene from the benzene.

9. A method for separating acetylene from admixture with other gases comprising intimately l contacting the gaseous mixture with an aqueous solution of glycolonitrile, separating the contacted gaseous mixture from the aqueous solution, co:ntacting the separated aqueous solution E with benzene, separating the contacted benzene from the aqueous solution, distilling acetylene from the separated benzene as the main product of the process.

10. A method for separating acetylene from admixture with other gases comprising intimately contacting the gaseous. mixture with an aque ous solution of glycolonitrile at a superatmospheric pressure and at atmospheric temperature, separating the contacted gaseous mixture from the aqueous solution, contacting the separated aqueous solution with benzene at atmospheric temperature, separating the contacted benzene from said aqueous solution, distilling the acetylene from the separated benzene, recovering the distilled acetylene as the main product of the process, and reusing the last mentioned aqueous solution and benzene as the first mentioned aqueous solution and benzene, respectively.

11. A method for separating acetylene from admixture with other gases comprising intimately contacting the gaseous mixture with an aquesolution with benzene, separating the contacted benzene from the aqueous solution, distilling acetylene from the separated benzene as the main product of the process.

13. A method for separating acetylene from admixture with other gases comprising intimately contacting the gaseous mixture with an aqueous solution of glycolonitrile acidified with phosphoric acid to a pH of 2% to 3 at a super- 'atmosphericpressure and at atmospheric temperature, separating the contacted gaseous mixture from the aqueous solution, contacting the separated aqueous solution with benzene at atmospheric temperature, separating the contacted benzene from said aqueous solution,

distilling the acetylene from the separated benzene, recovering the distilled acetylene as the main product of the process, and reusing the last mentioned aqueous solution and benzene as the first mentioned aqueous solution and benezene, respectively.

SAM P. ROBINSON.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,882,978 Schmidt et a1 Oct. 18, 1932 1,946,489 De Jahn Feb. 13, 1934 1,965,100 Groll et al. July 3, 1934 2,217,429 Balcar Oct. 8, 1940 2,371,908 Morris et a1 Mar. 20, 1945 FOREIGN PATENTS Number Country Date 331,610 Great Britain July 10, 1930 400,054 Great Britain Oct. 19, 1933 548,733 Great Britain Oct. 22, 1942 608,091 Great Britain Sept. 9, 1948. 

1. A METHOD FOR SEPARATING ACETYLENE FROM ADMIXTURE WITH GASES WITH WHICH ACETYLENE IS NORMALLY PRODUCED COMPRISING CONTACTING SAID ADMIXTURE OF GASES WITH A REAGENT COMPRISING AN AQUEOUS SOLUTION OF GLYCOLONITRILE ACIDIFIED WITH A NONVOLATILE MINERAL ACID TO A PH OF 2 1/2 TO 3, SEPARATING THE RESULTING SOLUTION FROM THE GASES AND RECOVERING ACETYLENE FROM SAID RESULTING SOLUTION. 